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/** @file pars/pars0opt.cc
 Simple SQL optimizer

 Created 12/21/1997 Heikki Tuuri
 *******************************************************/

#include "pars0opt.h"

#include <stddef.h>

#include "dict0boot.h"
#include "dict0dict.h"
#include "dict0mem.h"
#include "lock0lock.h"
#include "pars0grm.h"
#include "pars0pars.h"
#include "que0que.h"
#include "row0ins.h"
#include "row0sel.h"
#include "row0upd.h"

#define OPT_EQUAL 1      /* comparison by = */
#define OPT_COMPARISON 2 /* comparison by <, >, <=, or >= */

#define OPT_NOT_COND 1
#define OPT_END_COND 2
#define OPT_TEST_COND 3
#define OPT_SCROLL_COND 4

/** Inverts a comparison operator.
 @return the equivalent operator when the order of the arguments is switched */
static int opt_invert_cmp_op(int op) /*!< in: operator */
{
  if (op == '<') {
    return ('>');
  } else if (op == '>') {
    return ('<');
  } else if (op == '=') {
    return ('=');
  } else if (op == PARS_LE_TOKEN) {
    return (PARS_GE_TOKEN);
  } else if (op == PARS_GE_TOKEN) {
    return (PARS_LE_TOKEN);
  } else {
    /* TODO: LIKE operator */
    ut_error;
  }
}

/** Checks if the value of an expression can be calculated BEFORE the nth table
 in a join is accessed. If this is the case, it can possibly be used in an
 index search for the nth table.
 @return true if already determined */
static bool opt_check_exp_determined_before(
    que_node_t *exp,      /*!< in: expression */
    sel_node_t *sel_node, /*!< in: select node */
    ulint nth_table)      /*!< in: nth table will be accessed */
{
  func_node_t *func_node;
  sym_node_t *sym_node;
  dict_table_t *table;
  que_node_t *arg;
  ulint i;

  ut_ad(exp && sel_node);

  if (que_node_get_type(exp) == QUE_NODE_FUNC) {
    func_node = static_cast<func_node_t *>(exp);

    arg = func_node->args;

    while (arg) {
      if (!opt_check_exp_determined_before(arg, sel_node, nth_table)) {
        return false;
      }

      arg = que_node_get_next(arg);
    }

    return true;
  }

  ut_a(que_node_get_type(exp) == QUE_NODE_SYMBOL);

  sym_node = static_cast<sym_node_t *>(exp);

  if (sym_node->token_type != SYM_COLUMN) {
    return true;
  }

  for (i = 0; i < nth_table; i++) {
    table = sel_node_get_nth_plan(sel_node, i)->table;

    if (sym_node->table == table) {
      return true;
    }
  }

  return false;
}

/** Looks in a comparison condition if a column value is already restricted by
 it BEFORE the nth table is accessed.
 @return expression restricting the value of the column, or NULL if not known */
static que_node_t *opt_look_for_col_in_comparison_before(
    ulint cmp_type,           /*!< in: OPT_EQUAL, OPT_COMPARISON */
    ulint col_no,             /*!< in: column number */
    func_node_t *search_cond, /*!< in: comparison condition */
    sel_node_t *sel_node,     /*!< in: select node */
    ulint nth_table,          /*!< in: nth table in a join (a query
                              from a single table is considered a
                              join of 1 table) */
    ulint *op)                /*!< out: comparison operator ('=',
                              PARS_GE_TOKEN, ... ); this is inverted
                              if the column appears on the right
                              side */
{
  sym_node_t *sym_node;
  dict_table_t *table;
  que_node_t *exp;
  que_node_t *arg;

  ut_ad(search_cond);

  ut_a((search_cond->func == '<') || (search_cond->func == '>') ||
       (search_cond->func == '=') || (search_cond->func == PARS_GE_TOKEN) ||
       (search_cond->func == PARS_LE_TOKEN) ||
       (search_cond->func == PARS_LIKE_TOKEN_EXACT) ||
       (search_cond->func == PARS_LIKE_TOKEN_PREFIX) ||
       (search_cond->func == PARS_LIKE_TOKEN_SUFFIX) ||
       (search_cond->func == PARS_LIKE_TOKEN_SUBSTR));

  table = sel_node_get_nth_plan(sel_node, nth_table)->table;

  if ((cmp_type == OPT_EQUAL) && (search_cond->func != '=') &&
      (search_cond->func != PARS_LIKE_TOKEN_EXACT) &&
      (search_cond->func != PARS_LIKE_TOKEN_PREFIX)) {
    return (nullptr);

  } else if ((cmp_type == OPT_COMPARISON) && (search_cond->func != '<') &&
             (search_cond->func != '>') &&
             (search_cond->func != PARS_GE_TOKEN) &&
             (search_cond->func != PARS_LE_TOKEN) &&
             (search_cond->func != PARS_LIKE_TOKEN_PREFIX) &&
             (search_cond->func != PARS_LIKE_TOKEN_SUFFIX)) {
    return (nullptr);
  }

  arg = search_cond->args;

  if (que_node_get_type(arg) == QUE_NODE_SYMBOL) {
    sym_node = static_cast<sym_node_t *>(arg);

    if ((sym_node->token_type == SYM_COLUMN) && (sym_node->table == table) &&
        (sym_node->col_no == col_no)) {
      /* sym_node contains the desired column id */

      /* Check if the expression on the right side of the
      operator is already determined */

      exp = que_node_get_next(arg);

      if (opt_check_exp_determined_before(exp, sel_node, nth_table)) {
        *op = search_cond->func;

        return (exp);
      }
    }
  }

  exp = search_cond->args;
  arg = que_node_get_next(arg);

  if (que_node_get_type(arg) == QUE_NODE_SYMBOL) {
    sym_node = static_cast<sym_node_t *>(arg);

    if ((sym_node->token_type == SYM_COLUMN) && (sym_node->table == table) &&
        (sym_node->col_no == col_no)) {
      if (opt_check_exp_determined_before(exp, sel_node, nth_table)) {
        *op = opt_invert_cmp_op(search_cond->func);

        return (exp);
      }
    }
  }

  return (nullptr);
}

/** Looks in a search condition if a column value is already restricted by the
 search condition BEFORE the nth table is accessed. Takes into account that
 if we will fetch in an ascending order, we cannot utilize an upper limit for
 a column value; in a descending order, respectively, a lower limit.
 @return expression restricting the value of the column, or NULL if not known */
static que_node_t *opt_look_for_col_in_cond_before(
    ulint cmp_type,           /*!< in: OPT_EQUAL, OPT_COMPARISON */
    ulint col_no,             /*!< in: column number */
    func_node_t *search_cond, /*!< in: search condition or NULL */
    sel_node_t *sel_node,     /*!< in: select node */
    ulint nth_table,          /*!< in: nth table in a join (a query
                              from a single table is considered a
                              join of 1 table) */
    ulint *op)                /*!< out: comparison operator ('=',
                              PARS_GE_TOKEN, ... ) */
{
  func_node_t *new_cond;
  que_node_t *exp;

  if (search_cond == nullptr) {
    return (nullptr);
  }

  ut_a(que_node_get_type(search_cond) == QUE_NODE_FUNC);
  ut_a(search_cond->func != PARS_OR_TOKEN);
  ut_a(search_cond->func != PARS_NOT_TOKEN);

  if (search_cond->func == PARS_AND_TOKEN) {
    new_cond = static_cast<func_node_t *>(search_cond->args);

    exp = opt_look_for_col_in_cond_before(cmp_type, col_no, new_cond, sel_node,
                                          nth_table, op);
    if (exp) {
      return (exp);
    }

    new_cond = static_cast<func_node_t *>(que_node_get_next(new_cond));

    exp = opt_look_for_col_in_cond_before(cmp_type, col_no, new_cond, sel_node,
                                          nth_table, op);
    return (exp);
  }

  exp = opt_look_for_col_in_comparison_before(cmp_type, col_no, search_cond,
                                              sel_node, nth_table, op);
  if (exp == nullptr) {
    return (nullptr);
  }

  /* If we will fetch in an ascending order, we cannot utilize an upper
  limit for a column value; in a descending order, respectively, a lower
  limit */

  if (sel_node->asc && ((*op == '<') || (*op == PARS_LE_TOKEN))) {
    return (nullptr);

  } else if (!sel_node->asc && ((*op == '>') || (*op == PARS_GE_TOKEN))) {
    return (nullptr);
  }

  return (exp);
}

/** Calculates the goodness for an index according to a select node. The
 goodness is 4 times the number of first fields in index whose values we
 already know exactly in the query. If we have a comparison condition for
 an additional field, 2 point are added. If the index is unique, and we know
 all the unique fields for the index we add 1024 points. For a clustered index
 we add 1 point.
 @return goodness */
static ulint opt_calc_index_goodness(
    dict_index_t *index,     /*!< in: index */
    sel_node_t *sel_node,    /*!< in: parsed select node */
    ulint nth_table,         /*!< in: nth table in a join */
    que_node_t **index_plan, /*!< in/out: comparison expressions for
                             this index */
    ulint *last_op)          /*!< out: last comparison operator, if
                             goodness > 1 */
{
  que_node_t *exp;
  ulint goodness;
  ulint n_fields;
  ulint col_no;
  ulint op;
  ulint j;

  /* At least for now we don't support using FTS indexes, or
  virtual index for queries done through InnoDB's own SQL parser. */
  if (dict_index_is_online_ddl(index) || (index->type & DICT_FTS) ||
      dict_index_has_virtual(index)) {
    return (0);
  }

  goodness = 0;

  /* Note that as higher level node pointers in the B-tree contain
  page addresses as the last field, we must not put more fields in
  the search tuple than dict_index_get_n_unique_in_tree(index); see
  the note in btr_cur_search_to_nth_level. */

  n_fields = dict_index_get_n_unique_in_tree(index);

  for (j = 0; j < n_fields; j++) {
    if (!index->get_field(j)->is_ascending) {
      /* The internal InnoDB SQL parser does not
      work on indexes with descending order. */
      return (0);
    }

    col_no = index->get_col_no(j);

    exp = opt_look_for_col_in_cond_before(
        OPT_EQUAL, col_no, static_cast<func_node_t *>(sel_node->search_cond),
        sel_node, nth_table, &op);
    if (exp) {
      /* The value for this column is exactly known already
      at this stage of the join */

      index_plan[j] = exp;
      *last_op = op;
      goodness += 4;
    } else {
      /* Look for non-equality comparisons */

      exp = opt_look_for_col_in_cond_before(
          OPT_COMPARISON, col_no,
          static_cast<func_node_t *>(sel_node->search_cond), sel_node,
          nth_table, &op);
      if (exp) {
        index_plan[j] = exp;
        *last_op = op;
        goodness += 2;
      }

      break;
    }
  }

  if (goodness >= 4 * dict_index_get_n_unique(index)) {
    goodness += 1024;

    if (index->is_clustered()) {
      goodness += 1024;
    }
  }

  /* We have to test for goodness here, as last_op may not be set */
  if (goodness && index->is_clustered()) {
    goodness++;
  }

  return (goodness);
}

/** Calculates the number of matched fields based on an index goodness.
 @return number of exactly or partially matched fields */
static inline ulint opt_calc_n_fields_from_goodness(
    ulint goodness) /*!< in: goodness */
{
  return (((goodness % 1024) + 2) / 4);
}

/** Converts a comparison operator to the corresponding search mode PAGE_CUR_GE,
 ...
 @return search mode */
static inline page_cur_mode_t opt_op_to_search_mode(
    bool asc, /*!< in: true if the rows should be fetched in an
               ascending order */
    ulint op) /*!< in: operator '=', PARS_GE_TOKEN, ... */
{
  if (op == '=' || op == PARS_LIKE_TOKEN_EXACT ||
      op == PARS_LIKE_TOKEN_PREFIX || op == PARS_LIKE_TOKEN_SUFFIX ||
      op == PARS_LIKE_TOKEN_SUBSTR) {
    if (asc) {
      return (PAGE_CUR_GE);
    } else {
      return (PAGE_CUR_LE);
    }
  } else if (op == '<') {
    ut_a(!asc);
    return (PAGE_CUR_L);
  } else if (op == '>') {
    ut_a(asc);
    return (PAGE_CUR_G);
  } else if (op == PARS_GE_TOKEN) {
    ut_a(asc);
    return (PAGE_CUR_GE);
  } else if (op == PARS_LE_TOKEN) {
    ut_a(!asc);
    return (PAGE_CUR_LE);
  } else {
    ut_error;
  }
}

/** Determines if a node is an argument node of a function node.
 @return true if is an argument */
static bool opt_is_arg(que_node_t *arg_node, /*!< in: possible argument node */
                       func_node_t *func_node) /*!< in: function node */
{
  que_node_t *arg;

  arg = func_node->args;

  while (arg) {
    if (arg == arg_node) {
      return true;
    }

    arg = que_node_get_next(arg);
  }

  return false;
}

/** Decides if the fetching of rows should be made in a descending order, and
 also checks that the chosen query plan produces a result which satisfies
 the order-by. */
static void opt_check_order_by(
    sel_node_t *sel_node) /*!< in: select node; asserts an error
                          if the plan does not agree with the
                          order-by */
{
  order_node_t *order_node;
  dict_table_t *order_table;
  ulint order_col_no;
  plan_t *plan;
  ulint i;

  if (!sel_node->order_by) {
    return;
  }

  order_node = sel_node->order_by;
  order_col_no = order_node->column->col_no;
  order_table = order_node->column->table;

  /* If there is an order-by clause, the first non-exactly matched field
  in the index used for the last table in the table list should be the
  column defined in the order-by clause, and for all the other tables
  we should get only at most a single row, otherwise we cannot presently
  calculate the order-by, as we have no sort utility */

  for (i = 0; i < sel_node->n_tables; i++) {
    plan = sel_node_get_nth_plan(sel_node, i);

    if (i < sel_node->n_tables - 1) {
      ut_a(dict_index_get_n_unique(plan->index) <= plan->n_exact_match);
    } else {
      ut_a(plan->table == order_table);

      ut_a((dict_index_get_n_unique(plan->index) <= plan->n_exact_match) ||
           (plan->index->get_col_no(plan->n_exact_match) == order_col_no));
    }
  }
}

/** Optimizes a select. Decides which indexes to tables to use. The tables
 are accessed in the order that they were written to the FROM part in the
 select statement. */
static void opt_search_plan_for_table(
    sel_node_t *sel_node, /*!< in: parsed select node */
    ulint i,              /*!< in: this is the ith table */
    dict_table_t *table)  /*!< in: table */
{
  plan_t *plan;
  dict_index_t *index;
  dict_index_t *best_index;
  ulint n_fields;
  ulint goodness;
  ulint last_op = 75946965; /* Eliminate a Purify
                            warning */
  ulint best_goodness;
  ulint best_last_op = 0; /* remove warning */
  que_node_t *index_plan[256];
  que_node_t *best_index_plan[256];

  plan = sel_node_get_nth_plan(sel_node, i);

  plan->table = table;
  plan->asc = sel_node->asc;
  plan->pcur_is_open = false;
  plan->cursor_at_end = false;

  /* Calculate goodness for each index of the table */

  index = table->first_index();
  best_index = index; /* Eliminate compiler warning */
  best_goodness = 0;

  do {
    goodness =
        opt_calc_index_goodness(index, sel_node, i, index_plan, &last_op);
    if (goodness > best_goodness) {
      best_index = index;
      best_goodness = goodness;
      n_fields = opt_calc_n_fields_from_goodness(goodness);

      ut_memcpy(best_index_plan, index_plan, n_fields * sizeof(void *));
      best_last_op = last_op;
    }

    dict_table_next_uncorrupted_index(index);
  } while (index);

  plan->index = best_index;

  n_fields = opt_calc_n_fields_from_goodness(best_goodness);

  if (n_fields == 0) {
    plan->tuple = nullptr;
    plan->n_exact_match = 0;
  } else {
    plan->tuple = dtuple_create(pars_sym_tab_global->heap, n_fields);
    dict_index_copy_types(plan->tuple, plan->index, n_fields);

    plan->tuple_exps = static_cast<que_node_t **>(
        mem_heap_alloc(pars_sym_tab_global->heap, n_fields * sizeof(void *)));

    ut_memcpy(plan->tuple_exps, best_index_plan, n_fields * sizeof(void *));
    if (best_last_op == '=' || best_last_op == PARS_LIKE_TOKEN_EXACT ||
        best_last_op == PARS_LIKE_TOKEN_PREFIX ||
        best_last_op == PARS_LIKE_TOKEN_SUFFIX ||
        best_last_op == PARS_LIKE_TOKEN_SUBSTR) {
      plan->n_exact_match = n_fields;
    } else {
      plan->n_exact_match = n_fields - 1;
    }

    plan->mode = opt_op_to_search_mode(sel_node->asc, best_last_op);
  }

  if (best_index->is_clustered() &&
      (plan->n_exact_match >= dict_index_get_n_unique(best_index))) {
    plan->unique_search = true;
  } else {
    plan->unique_search = false;
  }

  plan->old_vers_heap = nullptr;

  plan->pcur.init();
  plan->clust_pcur.init();
}

/** Looks at a comparison condition and decides if it can, and need, be tested
 for a table AFTER the table has been accessed.
 @return OPT_NOT_COND if not for this table, else OPT_END_COND,
 OPT_TEST_COND, or OPT_SCROLL_COND, where the last means that the
 condition need not be tested, except when scroll cursors are used */
static ulint opt_classify_comparison(
    sel_node_t *sel_node, /*!< in: select node */
    ulint i,              /*!< in: ith table in the join */
    func_node_t *cond)    /*!< in: comparison condition */
{
  plan_t *plan;
  ulint n_fields;
  ulint op;
  ulint j;

  ut_ad(cond && sel_node);

  plan = sel_node_get_nth_plan(sel_node, i);

  /* Check if the condition is determined after the ith table has been
  accessed, but not after the i - 1:th */

  if (!opt_check_exp_determined_before(cond, sel_node, i + 1)) {
    return (OPT_NOT_COND);
  }

  if ((i > 0) && opt_check_exp_determined_before(cond, sel_node, i)) {
    return (OPT_NOT_COND);
  }

  /* If the condition is an exact match condition used in constructing
  the search tuple, it is classified as OPT_END_COND */

  if (plan->tuple) {
    n_fields = dtuple_get_n_fields(plan->tuple);
  } else {
    n_fields = 0;
  }

  for (j = 0; j < plan->n_exact_match; j++) {
    if (opt_is_arg(plan->tuple_exps[j], cond)) {
      return (OPT_END_COND);
    }
  }

  /* If the condition is an non-exact match condition used in
  constructing the search tuple, it is classified as OPT_SCROLL_COND.
  When the cursor is positioned, and if a non-scroll cursor is used,
  there is no need to test this condition; if a scroll cursor is used
  the testing is necessary when the cursor is reversed. */

  if ((n_fields > plan->n_exact_match) &&
      opt_is_arg(plan->tuple_exps[n_fields - 1], cond)) {
    return (OPT_SCROLL_COND);
  }

  /* If the condition is a non-exact match condition on the first field
  in index for which there is no exact match, and it limits the search
  range from the opposite side of the search tuple already BEFORE we
  access the table, it is classified as OPT_END_COND */

  if ((dict_index_get_n_fields(plan->index) > plan->n_exact_match) &&
      opt_look_for_col_in_comparison_before(
          OPT_COMPARISON, plan->index->get_col_no(plan->n_exact_match), cond,
          sel_node, i, &op)) {
    if (sel_node->asc && ((op == '<') || (op == PARS_LE_TOKEN))) {
      return (OPT_END_COND);
    }

    if (!sel_node->asc && ((op == '>') || (op == PARS_GE_TOKEN))) {
      return (OPT_END_COND);
    }
  }

  /* Otherwise, cond is classified as OPT_TEST_COND */

  return (OPT_TEST_COND);
}

/** Recursively looks for test conditions for a table in a join. */
static void opt_find_test_conds(sel_node_t *sel_node, /*!< in: select node */
                                ulint i, /*!< in: ith table in the join */
                                func_node_t *cond) /*!< in: conjunction of
                                                   search conditions or NULL */
{
  func_node_t *new_cond;
  ulint fclass;
  plan_t *plan;

  if (cond == nullptr) {
    return;
  }

  if (cond->func == PARS_AND_TOKEN) {
    new_cond = static_cast<func_node_t *>(cond->args);

    opt_find_test_conds(sel_node, i, new_cond);

    new_cond = static_cast<func_node_t *>(que_node_get_next(new_cond));

    opt_find_test_conds(sel_node, i, new_cond);

    return;
  }

  plan = sel_node_get_nth_plan(sel_node, i);

  fclass = opt_classify_comparison(sel_node, i, cond);

  if (fclass == OPT_END_COND) {
    UT_LIST_ADD_LAST(plan->end_conds, cond);

  } else if (fclass == OPT_TEST_COND) {
    UT_LIST_ADD_LAST(plan->other_conds, cond);
  }
}

/** Normalizes a list of comparison conditions so that a column of the table
 appears on the left side of the comparison if possible. This is accomplished
 by switching the arguments of the operator. */
static void opt_normalize_cmp_conds(
    func_node_t *cond,   /*!< in: first in a list of comparison
                         conditions, or NULL */
    dict_table_t *table) /*!< in: table */
{
  que_node_t *arg1;
  que_node_t *arg2;
  sym_node_t *sym_node;

  while (cond) {
    arg1 = cond->args;
    arg2 = que_node_get_next(arg1);

    if (que_node_get_type(arg2) == QUE_NODE_SYMBOL) {
      sym_node = static_cast<sym_node_t *>(arg2);

      if ((sym_node->token_type == SYM_COLUMN) && (sym_node->table == table)) {
        /* Switch the order of the arguments */

        cond->args = arg2;
        que_node_list_add_last(nullptr, arg2);
        que_node_list_add_last(arg2, arg1);

        /* Invert the operator */
        cond->func = opt_invert_cmp_op(cond->func);
      }
    }

    cond = UT_LIST_GET_NEXT(cond_list, cond);
  }
}

/** Finds out the search condition conjuncts we can, and need, to test as the
 ith table in a join is accessed. The search tuple can eliminate the need to
 test some conjuncts. */
static void opt_determine_and_normalize_test_conds(
    sel_node_t *sel_node, /*!< in: select node */
    ulint i)              /*!< in: ith table in the join */
{
  plan_t *plan;

  plan = sel_node_get_nth_plan(sel_node, i);

  UT_LIST_INIT(plan->end_conds);
  UT_LIST_INIT(plan->other_conds);

  /* Recursively go through the conjuncts and classify them */

  opt_find_test_conds(sel_node, i,
                      static_cast<func_node_t *>(sel_node->search_cond));

  opt_normalize_cmp_conds(UT_LIST_GET_FIRST(plan->end_conds), plan->table);

  ut_a(UT_LIST_GET_LEN(plan->end_conds) >= plan->n_exact_match);
}

/** Looks for occurrences of the columns of the table in the query subgraph and
 adds them to the list of columns if an occurrence of the same column does not
 already exist in the list. If the column is already in the list, puts a value
 indirection to point to the occurrence in the column list, except if the
 column occurrence we are looking at is in the column list, in which case
 nothing is done. */
void opt_find_all_cols(
    bool copy_val,             /*!< in: if true, new found columns are
                                added as columns to copy */
    dict_index_t *index,       /*!< in: index of the table to use */
    sym_node_list_t *col_list, /*!< in: base node of a list where
                               to add new found columns */
    plan_t *plan,              /*!< in: plan or NULL */
    que_node_t *exp)           /*!< in: expression or condition or
                               NULL */
{
  func_node_t *func_node;
  que_node_t *arg;
  sym_node_t *sym_node;
  ulint col_pos;

  if (exp == nullptr) {
    return;
  }

  if (que_node_get_type(exp) == QUE_NODE_FUNC) {
    func_node = static_cast<func_node_t *>(exp);

    for (arg = func_node->args; arg != nullptr; arg = que_node_get_next(arg)) {
      opt_find_all_cols(copy_val, index, col_list, plan, arg);
    }

    return;
  }

  ut_a(que_node_get_type(exp) == QUE_NODE_SYMBOL);

  sym_node = static_cast<sym_node_t *>(exp);

  if (sym_node->token_type != SYM_COLUMN) {
    return;
  }

  if (sym_node->table != index->table) {
    return;
  }

  /* Look for an occurrence of the same column in the plan column
  list */

  for (auto col_node : *col_list) {
    if (col_node->col_no == sym_node->col_no) {
      if (col_node == sym_node) {
        /* sym_node was already in a list: do
        nothing */

        return;
      }

      /* Put an indirection */
      sym_node->indirection = col_node;
      sym_node->alias = col_node;

      return;
    }
  }

  /* The same column did not occur in the list: add it */

  UT_LIST_ADD_LAST(*col_list, sym_node);

  sym_node->copy_val = copy_val;

  /* Fill in the field_no fields in sym_node */

  sym_node->field_nos[SYM_CLUST_FIELD_NO] =
      index->table->first_index()->get_col_pos(sym_node->col_no);
  if (!index->is_clustered()) {
    ut_a(plan);

    col_pos = index->get_col_pos(sym_node->col_no);

    if (col_pos == ULINT_UNDEFINED) {
      plan->must_get_clust = true;
    }

    sym_node->field_nos[SYM_SEC_FIELD_NO] = col_pos;
  }
}

/** Looks for occurrences of the columns of the table in conditions which are
 not yet determined AFTER the join operation has fetched a row in the ith
 table. The values for these column must be copied to dynamic memory for
 later use. */
static void opt_find_copy_cols(
    sel_node_t *sel_node,     /*!< in: select node */
    ulint i,                  /*!< in: ith table in the join */
    func_node_t *search_cond) /*!< in: search condition or NULL */
{
  func_node_t *new_cond;
  plan_t *plan;

  if (search_cond == nullptr) {
    return;
  }

  ut_ad(que_node_get_type(search_cond) == QUE_NODE_FUNC);

  if (search_cond->func == PARS_AND_TOKEN) {
    new_cond = static_cast<func_node_t *>(search_cond->args);

    opt_find_copy_cols(sel_node, i, new_cond);

    new_cond = static_cast<func_node_t *>(que_node_get_next(new_cond));

    opt_find_copy_cols(sel_node, i, new_cond);

    return;
  }

  if (!opt_check_exp_determined_before(search_cond, sel_node, i + 1)) {
    /* Any ith table columns occurring in search_cond should be
    copied, as this condition cannot be tested already on the
    fetch from the ith table */

    plan = sel_node_get_nth_plan(sel_node, i);

    opt_find_all_cols(true, plan->index, &(plan->columns), plan, search_cond);
  }
}

/** Classifies the table columns according to whether we use the column only
 while holding the latch on the page, or whether we have to copy the column
 value to dynamic memory. Puts the first occurrence of a column to either list
 in the plan node, and puts indirections to later occurrences of the column. */
static void opt_classify_cols(sel_node_t *sel_node, /*!< in: select node */
                              ulint i) /*!< in: ith table in the join */
{
  plan_t *plan;
  que_node_t *exp;

  plan = sel_node_get_nth_plan(sel_node, i);

  /* The final value of the following field will depend on the
  environment of the select statement: */

  plan->must_get_clust = false;

  UT_LIST_INIT(plan->columns);

  /* All select list columns should be copied: therefore true as the
  first argument */

  for (exp = sel_node->select_list; exp != nullptr;
       exp = que_node_get_next(exp)) {
    opt_find_all_cols(true, plan->index, &(plan->columns), plan, exp);
  }

  opt_find_copy_cols(sel_node, i,
                     static_cast<func_node_t *>(sel_node->search_cond));

  /* All remaining columns in the search condition are temporary
  columns: therefore false */

  opt_find_all_cols(false, plan->index, &plan->columns, plan,
                    static_cast<func_node_t *>(sel_node->search_cond));
}

/** Fills in the info in plan which is used in accessing a clustered index
 record. The columns must already be classified for the plan node. */
static void opt_clust_access(sel_node_t *sel_node, /*!< in: select node */
                             ulint n) /*!< in: nth table in select */
{
  plan_t *plan;
  dict_table_t *table;
  dict_index_t *clust_index;
  dict_index_t *index;
  mem_heap_t *heap;
  ulint n_fields;
  ulint pos;
  ulint i;

  plan = sel_node_get_nth_plan(sel_node, n);

  index = plan->index;

  /* The final value of the following field depends on the environment
  of the select statement: */

  plan->no_prefetch = false;

  if (index->is_clustered()) {
    plan->clust_map = nullptr;
    plan->clust_ref = nullptr;

    return;
  }

  table = index->table;

  clust_index = table->first_index();

  n_fields = dict_index_get_n_unique(clust_index);

  heap = pars_sym_tab_global->heap;

  plan->clust_ref = dtuple_create(heap, n_fields);

  dict_index_copy_types(plan->clust_ref, clust_index, n_fields);

  plan->clust_map =
      static_cast<ulint *>(mem_heap_alloc(heap, n_fields * sizeof(ulint)));

  for (i = 0; i < n_fields; i++) {
    pos = dict_index_get_nth_field_pos(index, clust_index, i);

    ut_a(pos != ULINT_UNDEFINED);

    /* We optimize here only queries to InnoDB's internal system
    tables, and they should not contain column prefix indexes. */

    if (dict_is_old_sys_table(index->table->id) &&
        (index->get_field(pos)->prefix_len != 0 ||
         clust_index->get_field(i)->prefix_len != 0)) {
      ib::error(ER_IB_MSG_916) << "Error in pars0opt.cc: table "
                               << index->table->name << " has prefix_len != 0";
    }

    *(plan->clust_map + i) = pos;

    ut_ad(pos != ULINT_UNDEFINED);
  }
}

#ifdef UNIV_SQL_DEBUG
/** Print info of a query plan.
@param[in,out]  sel_node        select node */
static void opt_print_query_plan(sel_node_t *sel_node);
#endif

/** Optimizes a select. Decides which indexes to tables to use. The tables
 are accessed in the order that they were written to the FROM part in the
 select statement. */
void opt_search_plan(sel_node_t *sel_node) /*!< in: parsed select node */
{
  sym_node_t *table_node;
  dict_table_t *table;
  order_node_t *order_by;
  ulint i;

  sel_node->plans = static_cast<plan_t *>(mem_heap_alloc(
      pars_sym_tab_global->heap, sel_node->n_tables * sizeof(plan_t)));

  /* Analyze the search condition to find out what we know at each
  join stage about the conditions that the columns of a table should
  satisfy */

  table_node = sel_node->table_list;

  if (sel_node->order_by == nullptr) {
    sel_node->asc = true;
  } else {
    order_by = sel_node->order_by;

    sel_node->asc = order_by->asc;
  }

  for (i = 0; i < sel_node->n_tables; i++) {
    table = table_node->table;

    /* Choose index through which to access the table */

    opt_search_plan_for_table(sel_node, i, table);

    /* Determine the search condition conjuncts we can test at
    this table; normalize the end conditions */

    opt_determine_and_normalize_test_conds(sel_node, i);

    table_node = static_cast<sym_node_t *>(que_node_get_next(table_node));
  }

  table_node = sel_node->table_list;

  for (i = 0; i < sel_node->n_tables; i++) {
    /* Classify the table columns into those we only need to access
    but not copy, and to those we must copy to dynamic memory */

    opt_classify_cols(sel_node, i);

    /* Calculate possible info for accessing the clustered index
    record */

    opt_clust_access(sel_node, i);

    table_node = static_cast<sym_node_t *>(que_node_get_next(table_node));
  }

  /* Check that the plan obeys a possible order-by clause: if not,
  an assertion error occurs */

  opt_check_order_by(sel_node);

#ifdef UNIV_SQL_DEBUG
  opt_print_query_plan(sel_node);
#endif
}

#ifdef UNIV_SQL_DEBUG
/** Print info of a query plan.
@param[in,out]  sel_node        select node */
static void opt_print_query_plan(sel_node_t *sel_node) {
  plan_t *plan;
  ulint n_fields;
  ulint i;

  fputs("QUERY PLAN FOR A SELECT NODE\n", stderr);

  fputs(sel_node->asc ? "Asc. search; " : "Desc. search; ", stderr);

  if (sel_node->set_x_locks) {
    fputs("sets row x-locks; ", stderr);
    ut_a(sel_node->row_lock_mode == LOCK_X);
    ut_a(!sel_node->consistent_read);
  } else if (sel_node->consistent_read) {
    fputs("consistent read; ", stderr);
  } else {
    ut_a(sel_node->row_lock_mode == LOCK_S);
    fputs("sets row s-locks; ", stderr);
  }

  putc('\n', stderr);

  for (i = 0; i < sel_node->n_tables; i++) {
    plan = sel_node_get_nth_plan(sel_node, i);

    if (plan->tuple) {
      n_fields = dtuple_get_n_fields(plan->tuple);
    } else {
      n_fields = 0;
    }

    fprintf(stderr,
            "Index %s of table %s"
            "; exact m. %lu, match %lu, end conds %lu\n",
            plan->index->name(), plan->index->table_name,
            (unsigned long)plan->n_exact_match, (unsigned long)n_fields,
            (unsigned long)UT_LIST_GET_LEN(plan->end_conds));
  }
}
#endif /* UNIV_SQL_DEBUG */
